1. Field of the Invention
The present invention relates to microwave measurement systems and RF direction finding, and particularly to a microwave radio direction finding system that operates on multiple bands and that resolves direction in both the azimuth and elevation planes.
2. Description of the Related Art
Identifying the source location of an incoming radio frequency (RF) signal is called RF direction finding (DF). It is used to estimate the angle of arrival (AoA) of an incident RF signal(s). DF has been (and still is) of interest over the past few decades due to its potential applications, specifically in military applications, and also for non-military purposes. It has a wide range of applications, which include, but are not limited to, military aspects of identifying hostile transmissions, avionics, emergency services, and amateur radio use.
An RF direction finding (DF) system consists of an array of antennas followed by one or more receivers arranged in a way to determine the azimuth angle of a distant emitter. Fundamentally, in all direction finding (DF) systems, location of a target object is determined by angle-of-arrival (AoA) estimation. Classical techniques of RF direction finding are based on multiple antenna systems employing single or multiple receivers. Classical techniques, such as multiple-channel DF algorithms; Multiple Signal Classification (MUSIC), and Estimation of Signal Parameters via Rotational Invariance Technique (ESPRIT), use simultaneous phase information from each antenna to estimate the AoA of the signal of interest.
In many scenarios where mobile systems are needed, multiple receivers are impractical. Thus, single channel techniques are of interest, particularly in mobile scenarios. But most of the existing techniques for single channel direction finding are either older analog techniques or require extensive digital processing techniques. Thus, this limits the use of digital signal processing (DSP) techniques in handheld RF DF systems.
To overcome the extensive processing of RF direction finding DSP algorithms, microwave measurement-based six-port technology is used. These multiport measuring techniques are gaining wide acceptance due to their precision and due to lower processing requirements in microwave metrology. The six-port circuit was initially used as low cost alternative to a network analyzer. Additionally, a number of six-port circuits are designed to be used in beam direction finding systems. All of these systems are used to find the azimuth angle of a distant target object, but not the elevation angle (i.e., a single angle for the incoming wave).
Thus, a microwave radio direction finding system solving the aforementioned problems is desired.